Pipettes and capillary tubes have long been used to collect and dispense fluids. These devices are particularly useful for collecting blood samples.
Perhaps the most simple type of capillary tube and micropipette is simply a glass or hydrophilic plastic tube open at both ends. One end of the tube is placed against a incision, blood flows into the tube from the incision by capillary action. Upon collection of the desired quantity of blood one can cap the end of the tube opposite the collection end.
It has been proposed to provide a unitary, blow-molded, plastic capillary tube with a flexible bulb blown at the proximate end of the capillary tube. To dispense the blood from the tube one simply squeezes the bulb. This technique has several shortcomings. First, it is difficult to dispense precise amounts of fluid from the pipette using the bulb. Second, in order to collect blood into the capillary tube, the user must first squeeze the bulb, then place the distal end of the tube against the incision and allow the bulb to expand. This technique draws air as well as blood into the tube. Consequently, bubbles are frequently interspersed with the collected blood. When the blood is then dispensed from the tube, air bubbles may be ejected with the blood. Some blood tests are conducted by placing droplets of blood on a reagent strip. If the blood is ejected with air bubbles, insufficient and poorly reproducible quantities of blood are deposited onto the strip providing inaccurate readings. Furthermore, the bubbles may cause the blood to spatter and form aerosols.
In our U.S. Pat. No. 5,065,765 we disclose a self-sealing blood collection tube. This tube has a plug at one end having at least one air passage therethrough which seals upon contact with the fluid. The fluid can be dispensed from the tube by pushing the plug into and through the tube. Although this device is quite useful, the volume of fluid which can be collected in a single tube is set by the dimensions of the tube and cannot later be changed by the user. Moreover, a special plunger device is required to dispense fluid from this tube.
There is a need for a simple and inexpensive blood collection tube which can collect and dispense precise quantities of collected blood or other fluids.